Baking ambient occlusion gives odd black vortex output?
For some reason this seems to be caused by the wire material.

If you remove it by pressing the - button:



Then it works as expected:



This looks like a bug to me. You might want to consider reporting it to the tracker. I've since reported it here.



Also note that there are some internal faces and non-manifold geometry in your model, which can also result in some artifacts. Try pressing &#9096; Ctrl&#9095; Alt&#8679; ShiftM in edit mode to select problem spots.